1. Field of the Invention
The present invention relates to an image processing apparatus.
2. Related Background Art
Information constituting a page, prepared for example by a word processor or a desk-top publishing system, can be generally divided into "characters", "patterns" such as a circle or a straight line, and "images" generated for example by an image scanner. Examples of such information will be explained further with reference to FIG. 3, in which 301 indicates a one-page data prepared, for example, by a word processor or a desk-top publishing system. These "characters", "patterns" and "images" are transferred in the form of codes 302 to a next process. For encoding an "image", in the case of a multi-value color image, there is often employed an image compression method called ADCT. In the conventional method, the encoded data 302 are developed, at the image output, as a raster image in a page memory 303 representing the entire area of a page. Even in the case where two "image" codes are included as shown in 302, the use of said page memory allows, after the development of a first image by an ADCT process block, the development of a second image. Also the "character" and "pattern" are developed in this page memory. The data of one page is transmitted to a printer unit for image output.
However, such page memory as explained above, requires a large memory capacity. If the printer unit is of a low speed, the page memory can be composed for example of a rigid disk, but it is inevitably expensive. As an example, a printer unit employing four colors of C (cyan), M (magenta), Y (yellow) and K (black) with a resolving power of 400 DPI and a gradation of 8 bits per color, there is requires a RAM of about 60 Mbytes for an A4-sized image. For this reason there is conceived a system, as represented by 304 in FIG. 3, of dividing a page into laterally oblong segments and developing the codes in a band memory corresponding to a segment. The memory capacity can be reduced by such segmentation of a page. However, in such structure, there has not been satisfactory processing in the case where a page contains plural "images" as shown in FIG. 3. For example, referring to FIG. 4, in case an expander of compressed image expands a first image 402 in a considered segment 404, a, b, c, . . . in said image 402 signifies blocks each consisting of 8.times.8 pixels in the ADCT process. After successive expansions of blocks a, b, c, . . . , f, the next block expansion has to be conducted not on a block g but on a block j in a second image 404. However, satisfactory image expansion cannot be conducted because the processed image is switched from the first image to the second image.
Also the present inventor has found that a drawback is encountered if the boundary of such segment does not coincide with the boundary of a small block of the image expanded from a compressed code. In an image compression method such as ADCT, the image is processed in a block for example of 8.times.8 pixels. If the boundary of said block does not coincide with the boundary of segment, in a block containing the boundary of two adjacent blocks, the data processing in a portion belonging to the next block becomes a problem.